The I-535 High Bridge opened to traffic on December 2, 1961, replacing the Interstate Bridge. At just shy of 8,000 feet, this was the longest bridge in Minnesota when it opened. If you include the overland approaches, the overall bridge length is 10,775 feet. The bridge has since been renamed after John A. Blatnik, a champion of the High Bridge project.

A need for a new Duluth harbor crossing was seen as early as 1930. Local officials lobbied for a new bridge. Another concept that was put forward was a plan for a tunnel under the harbor, much like the I-10 George Wallace Tunnel in Mobile, Alabama. Between the depression and World War II, these proposals remained unfunded. The bridge issue surfaced again in the mid-1950s. This time, money was available though the Interstate Highway program. The route was designated I-535. Construction began in the late 1950s, with a grand opening in late 1961. The Interstate Bridge, located below and slightly east of the High Bridge, closed within a year of the opening of the new I-535 High Bridge.

The bridge was officially named after John A. Blatnik on September 24, 1971. Blatnik was born on the Iron Range. He served as state Senator from 1940 to 1944 and also served in the US Army Air Force. After WWII, Blatnik served in the US House of Representatives from 1947 to 1975. Blatnik also was a champion of the St. Lawrence Seaway project.

Major reconstruction of the Blatnik bridge occurred in 1992 and 1993. The major work was to widen the bridges to add room to the shoulders, and to install a center divider. There was also a three year project to paint the bridge from end to end.

While Minnesota has one entry in the National Bridge Inventory for the Blatnik Bridge, Wisconsin maintains 5 entries as follows:

 NBI #B16000500050000, 2,241 Feet, Girder Span, Crosses WI-35.
 NBI #B16000500020000, 697 Feet, Girder Span, Crosses Howards Pocket.
 NBI #B16000500030000, 1,884 Feet, Girder Span, Crosses Soo Line Railroad.
 NBI #B16000500010000, 1,140 Feet, Arch Span, Crosses St. Louis Bay.
 NBI #B16000500040000, 2,022 Feet, Girder Span, Crosses Garfield Ave.

If you add up these spans, you get 10,225 feet. This is 2,245 feet longer than what Minnesota reports in their NBI entry. Minnesota apparently does not count the bridge sections that cross WI-35 on the Superior end of the bridge. It is also possible that Minnesota recognizes a different northern endpoint for the bridge. As evidence, a photo below shows that there is landfill between the Blatnik Bridge and the Garfield Avenue Bridge. If Wisconsin considers the Garfield Avenue interchange to be part of the Blatnik Bridge, that could account for the 2,245 foot discrepancy.

In early 2008, the Minnesota state Department of Transportation started a program to inspect and audit all of the truss bridges in Minnesota. On May 6, 2008, MN-DOT announced that they discovered that structural load calculations had not been run on the bridge based on the modifications that were made in the early 1990s. As a result, the bridge might be unsafe. Once these calculations were completed, it was discovered that 16 critical gusset plates did not have a sufficient safety margin when the extra weight of the wider deck was factored in. As a result, two lanes of the bridge were closed. The bridge will remain open with on lane in each direction until the problem can be fixed. The fix turns out to be relatively simple. Each gusset plate will have a section of angle iron attached to increase its strength.

The photo above is looking north towards Duluth from the Harvest States grain elevator. It is amazing that there are relatively few locations to get a good unobstructed view of such a large structure. The photo below shows the Blatnik Bridge looking southbound from the Garfield Avenue exit ramp.

Two views of the main span from slightly different angles. These photos were taken from the DNR boat launch parking lot that sits directly under the north end of the structure. Notice that the truss section not only includes the main arch, but that the truss also extends back one span on each side of the main span. This is in contrast to the more modern Bong Bridge just upstream where the arch structure only covers the main span. Also notice the horizontal lines in the concrete on the piers. It appears that the piers may be made out of segments that were precast and installed in this location as part of assembly. Using such a strategy would have vastly shortened the time required to build the bridge.

Here are two photos taken from a distance, each showing a large portion of the bridge. The above photo was taken from the Bong Bridge by pointing a camera out of the passenger window of my truck. One can see a large ship passing under the main span. The large Harvest States elevator complex is on the right side of the photo. The photo below was shot from Thompson's Hill near the I-35 Rest Stop.

The remaining photos are of a typical crossing from Superior to Duluth. The photo above is the big green sign at the start of the bridge, indicating the start of Interstate 535. The grain elevator complex is the Harvest States Cooperative facility. Below is the initial upward climb from ground level to about the 90 foot level. It feels very much like the initial climb on a roller coaster. The speed limit is 55 MPH, which was raised from 45 MPH after the major rebuild in the early 1990s.

The photo above is reaching the top of initial climb. The photo below is the causeway turn over Howards Bay. Duluth can be seen in the background, and Minnesota Point is off to the right.

These two photos show the trip across Howard's Bay towards the final climb to the 125-foot level for them main span. The Cargil grain elevators are visible to the right of the highway. In addition, the General Mills elevator is visible in the distance on the photo below (below the yellow highway sign).

In these two photos, we cross into the main arch section, then pass through the arch. The suspension cables that holds up the roadway are clearly visible on the right side of the photos. The cables are installed in groups of four.

After passing though the arch, we start downhill into Duluth. This gives us a better view of the Duluth side of the harbor. The photo below shows the Garfield Avenue interchange. This is the only exit on I-535, and it provides access to the Duluth harbor waterfront and to the park under the Blatnik Bridge. That park includes the surviving section of the old Interstate Bridge.

Back on flat land, we are rapidly facing the choice of heading north on I-35 towards downtown Duluth, south on I-35, or staying on US-53 to go up Miller Hill towards the mall and airport area on top of the bluffs. The rail yard to the right is one of the many BNSF rail yards in the Twin Ports area. The photo below shows the Minnesota state line sign. While most states use steel signs for the state line, both Minnesota and Wisconsin put up monuments at the state line.

In the photo above, we take the I-35 north option towards downtown Duluth. Enger Tower can be seen on the top of the bluff. Enger Tower was built during the depression as a tourist attraction. The base of the tower sits 531 feet above the Lake Superior water level.

The photo below is merging onto I-35 heading northbound. I-35 was put though in the early and mid-1980s. The section at the far end of the photo running to Lake Street opened in 1986. The final sections past downtown opened in the early 1990s. The section in this photo is built on an old railroad switching yard. The state funded part of the building of the Pokegamma Rail Yard in Superior in order to get the lakefront land to build I-35.